Current tissue engineering applications use stem cells that must differentiate into specific cell types to form tissues and organs. Controlling the broad differentiation potential of stem cells in order to generate desired cell lineages is difficult using existing methods. Stem cells are generally positioned on a scaffold and various biochemical factors are added in order to steer the differentiation of the cells into the desired lineages. Lack of access to interior regions of tissues and organs increases the difficulty of exercising control over cell differentiation and tissue construction.